Increasingly dire warnings of the dangers of climate change by the world's scientific community combined with greater public awareness and concern over the issue has prompted increased momentum towards global regulation aimed at reducing man-made greenhouse gas (GHGs) emissions, most notably carbon dioxide. Ultimately, a significant cut in North American and global CO2 emissions will require reductions from the electricity production sector, the single largest source of CO2 worldwide. According to the International Energy Agency's (IEA) GHG Program, as of 2006 there were nearly 5,000 fossil fuel power plants worldwide generating nearly 11 billion tons of CO2, representing nearly 40% of total global anthropogenic CO2 emissions. Of these emissions from the power generation sector, 61% were from coal fired plants. Although the long-term agenda advocated by governments is replacement of fossil fuel generation by renewables, growing energy demand, combined to the enormous dependence on fossil generation in the near term dictates that this fossil base remain operational. Thus, to implement an effective GHG reduction system will require that the CO2 emissions generated by this sector be mitigated, with carbon capture and storage (CCS) providing one of the best known solutions.
The CCS process removes CO2 from a CO2 containing gas and involves the production of a highly concentrated CO2 gas stream which is compressed and transported to a geologic sequestration site. This site may be a depleted oil field, a saline aquifer or any suitable storage site. Sequestration in oceans and mineral carbonation are two alternate ways to sequester CO2 that are in the research phase. Captured CO2 can also be used for enhanced oil recovery or for carbonation of alkaline waste streams for sequestration as mineral solids.
Conventional technologies for CO2 capture are based primarily on the use of aqueous amine (e.g. alkanolamines) which is circulated through two main distinct units: an absorption unit coupled to a desorption (or stripping) unit. However in the context of low CO2 partial pressures encountered in gases from combustion, these conventional technologies give rise to processes with high energy penalty and thus high operational expenditure, as it is the case with monoethanolamine (MEA), or processes with high capital expenditure, as for the case of kinetically limited absorption solutions resulting in large equipment such as with methydiethanolamine (MDEA) for example. Higher pressure CO2 separation from process streams seen in H2 production or gasification is typically usually easier to achieve due to the higher pressures in such processes.
Carbonic anhydrase is an enzyme that has been used for CO2 absorption applications. Carbonic anhydrase is not just a single enzyme form, but a broad group of metalloproteins that exists in genetically unrelated families of isoforms, α, β, γ, δ and ϵ. Different classes, isoforms and variants of carbonic anhydrase have been used in order to catalyze the hydration reaction of CO2 into bicarbonate and hydrogen ions and the bicarbonate dehydration reaction into CO2 and water, as follows:CO2+H2OH++HCO3−  (Reaction 1)
Under optimum conditions, the catalyzed turnover rate of the hydration reaction can reach 1×106 molecules/second.
However, there are several challenges related to the use of carbonic anhydrase in CO2 capture operations. For instance, the temperature stability in time, the chemical resistance and the activity of the carbonic anhydrase under process conditions are factors that have an impact on process design, process performance and operating costs.
There is thus a need to overcome at least some of the challenges related to the use of carbonic anhydrase for CO2 capture.